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Engineering Mechanics
What is Mechanics ?
Mechanics is a science that describes or predicts the
conditions of rest or motion of bodies under the action of
forces.
Mechanics
Mechanics of
Rigid
Bodies
Statics
Mechanics of
Deformable
Bodies
Dynamics
Mechanics of Fluids
History
• Aristotle ( 384 -322 B.C.)
•Archimedes ( 287 – 212 B.C.)
•Isaac Newton ( 1642 – 1727)
•D’Lambert
•Lagrange
•Hamilton
•Albert Einstein ( Theory of Relativity - 1905)
Basic Concepts
Space : 3 dimensional
Position of point A is defined by three lengths measured
from the origin in three directions. (coordinates)
A
o
Unit of length is
meter (m)
Basic Concepts
Mass :
•a fundamental property of a body
•amount of matter in the body
•a numerical measure of its inertia
Unit of mass
is
kilogram (kg)
Force :
• the action of a body on another body
•it causes the body to accelerate, that is to change its velocity
• It can be applied by actual contact or at a distance
(gravitational forces, magnetic forces)
Basic Concepts
Force :
Force is defined by :
• its point of application
• its magnitude
• its direction
Unit of force is
newton (N)
30°
A
Defined by a vector
Basic Concepts
Resultant Force :
The total effect of two or more forces acting on a particle or a
body can be represented by a single force which is called
resultant force.
P
R
A
Q
Basic Concepts
Particle :
very small amount of matter which may be assumed to
occupy a single point in a space
Rigid Body
:
combination of a large number of particles
Basic Concepts
Newton’s Three Fundamental Laws:
If the resultant force on a particle is zero, then:
a. if it was at rest originally , it remains at rest
b. if it was in motion, its velocity doesn’t change
Basic Concepts
Newton’s Three Fundamental Laws:
2. If the resultant force is not zero, then it causes the
particle or the body to have an acceleration.
The amount of the acceleration is proportional to the
magnitude of the resultant and in the direction of the
resultant force
F=ma
F = resultant force acting on the particle
m = mass of the particle
a = acceleration of the particle
Basic Concepts (Reminder)
Speed
• Speed is the rate at which a particle changes its
position
• The distance taken in unit time (meters/second)
• It refers to how fast a particle is moving
• It is a scalar quantity.
• Direction doesn’t matter
Velocity
• Speed with defined direction
• Vector quantity
Basic Concepts (Reminder)
Acceleration
• the rate of change in velocity
• It refers to how fast a particle changes its velocity
• amount of change in velocity in unit time
(meters/second) / second = meters/ second squared)
m/s
s
=
m/ s
2
Basic Concepts
Newton’s Three Fundamental Laws:
3. The forces of action and reaction between bodies in
relation have the same magnitude, same line of
action but opposite direction.
Basic Concepts
Newton’s Law of Gravitation:
-F m
M
F
m,M : masses of particles
r : distance between particles
r
Two particles (bodies) attract each other mutually with
equal and opposite forces F and –F of magnitude F
Mm
F G 2
r
G : universal constant
Basic Concepts
Newton’s Law of Gravitation:
Special Case
Attraction of earth on a particle located on its surface
R : the radius of earth,
M: mass of earth
Mm
F G 2
R
F  g m W
Basic Concepts
Newton’s Law of Gravitation:
Special Case
F  g m W
Weight : W
the gravitational force applied on particle by the earth
F m a
F gm
g a
g  9.81 m / s 2
Systems Of Units
Time : second (s)
Original definition : 1 / 86400 of mean solar day
Official definition : 9,192,631,770 cycles of the radiation
corresponding to the transition between two levels of the
fundamental state of cesium-133 atom.
Length : meter (m)
Original definition : 1 / 10,000,000 of the distance from equator
to either pole
Official definition : 1,650,763.73 wavelengths of the orangered light corresponding to a certain transition in a atom of
krypton-86
Systems Of Units
Mass : kilogram (kg)
Original definition : mass of 0,001 m3 water
Official definition : mass of platinum-iridium standart
Force : newton (N)
The magnitude of force that gives an acceleration of 1 m / s
to a mass of 1 kg.
2
1 N = (1 kg) ( 1 m / s )
2
Systems Of Units
Weight : Newton (N)
the gravitational force applied on a body by the earth
W gm
g  9.81 m / s 2
m : the mass of particle ( kg)
The weight of a body of mass 1 kg :
W  g m  ( 9.81 m / s 2 ) (1 kg )  9.81 N
Systems Of Units
Homework
Review the other systems of units
•Units of Area
•Units of Volume
•etc